Molecular analysis of a new series of synovial sarcomas confirms that t(X;18)(p11.2;q11.2) breakpoints occur at two distinct regions on Xp designated SS1 and SS2. Breakpoint position correlates with tumor phenotype. Monophasic tumors with no evidence of glandular components have breakpoints within the SS2 region in Xp11.21, and biphasic tumors with a focal poorly differentiated or extensive glandular structure have breakpoints within the SS1 region in Xp11.23.